Inflatable safety restraint devices, or airbags, are mandatory on most new vehicles. Airbags are typically installed as part of a system with an airbag module in the steering wheel on the driver's side of car and in the dashboard on the passenger side of a car. In the event of an accident, a sensor within the vehicle measures abnormal deceleration and triggers the ignition of a charge contained within an inflator. Expanding gases from the charge travel through conduits and fill the airbags, which immediately inflate in front of the driver and passenger to protect them from harmful impact with the interior of the car. Typically, airbags are concealed within the vehicle trim to be invisible during normal vehicle operation.
The inflator is a critical part of the airbag assembly because it supplies the inflation gas needed to inflate the airbag cushion. The performance of the inflator is a key to effective airbag deployment. The airbag needs to deploy rapidly to be in place before motion of the vehicle occupants, but if deployment is too rapid, the result may be that the inflated airbag is too hard, thus failing to effectively cushion the occupants. Additionally, if the gases produced by the inflator are excessively hot or entrain too much debris, damage to the airbag may result. Thus, the gas output duration, volume, purity, and temperature are all important factors in the performance of the airbag system.
Typically, inflators are compressed gas, pyrotechnic, or hybrid inflators. “Compressed gas” inflators contain gas under pressure, while “pyrotechnic” inflators contain a pyrotechnic gas generant that ignites to produce the gas. “Hybrid” inflators typically use both compressed gas and a pyrotechnic charge. Some inflators are “dual stage,” meaning that they can receive two independent activation signals to enable production of a selectively variable quantity of inflation gas, and others have only a single stage. However, single stage inflators can have multiple timed events, such as the ignition of multiple separate pyrotechnic charges and/or the release of distinct volumes of compressed gas, that are all triggered by a single activation signal.
Inflators of all types are typically made from a wide variety of parts. Each inflator may contain a selection of chambers, diffusers, filters, frangible membranes, initiators, generants, baffles, and containers, attachment hardware, and other components. Each of these parts adds significantly to the cost of the inflator. Hence, the inflator typically makes up a large portion of the cost of an airbag assembly.
Additionally, a series of different manufacturing steps may be needed to manufacture each inflator. The quantity of steps involved not only further increases the cost of potential inflators, it also increases the likelihood of defects in material or workmanship in the finished inflator.